J. Am. Chem. Sot. 1990, 112, 5636-5637
5636
than the first row cobalt analogues. The difference in free energies of activation for ethyl migration in the Co complex 4 relative to the Rh analogue 8a of 8 kcal/mol corresponds to a rate difference of 105-106at 25 OC. The difference in A G * R . ~and ~ * AG*H.mig, AAG*, for the Rh systems is 10.3 kcal/mol, while this number is less for the cobalt systems, ca. 8-6 kcal/mol. This is consistent with the expectation that as the barriers to H and R migration decrease, the difference between them will decrease. The detailed comparisons that can now be made between the Rh and Co systems provide quantitative support for our earlier s~ggestion"~ that barriers for alkyl migrations will be lower for cases in which the hydride analogues exist as bridged (agostic) isomers rather than as terminal hydrides. Acknowledgment is made to the National Science Foundation (Grant No. CHE-8705534) for support of this research. Supplementary Material Available: Description of the lowtemperature 13CN M R kinetics experiment, sample spectra, and kinetic plots (5 pages). Ordering information is given on any current masthead page.
Synthesis of Homoleptic Silylphosphido Complexes (M[P(SiMe3)2~p-P(SiMe3)2]]2, Where M = Zn and Cd, and Their Use in Metalloorganic Routes to Cd3P2and MGeP,
127 (10
ORTEP representation of (Zn[P(SiMe3)2][pP(SiMe3) (1); hydrogen atoms were omitted for clarity. Selected distances Zn-P(1), 2.421 (I); Zn-P(2), 2.295 (1); Zn-P(lA), 2.419 (1); Zn-Zn(A), 3.401 ( I ) . Selected angles (deg): P(I)-Zn-P(2), 124.1 ( I ) ; P(I)-Zn-P(IA), 90.7 (1); P(2)-Zn-P(IA), 144.9 ( I ) ; Zn-P(1)-Zn(A), 89.3 ( I ) ; Zn-P(2)-Si(3), 107.0 ( I ) ; Zn-P(2)-Si(4), 103.6 (4); Si(3)-P(2)-Si(4), 106.2 ( I ) .
structure of (Zn[P(SiMe3),] [p-P(SiMe,),]), (1) is shown in Figure (Cd[P(SiMe3)2][p-P(SiMe3),]lz (2) is isomorphous. Compounds 1 and 2 appear to be the first homoleptic phosphido complexes of zinc5 and cadmium6 and the first homoleptic P(SiMe3)2complexes in general.' M[N(SiMe,),],
Subhash C. Goel, Michael Y. Chiang, and William E. Buhro*
Department of Chemistry, Washington University St. Louis, Missouri 631 30 Received January 16, 1990 Several recent reports have described solution-phase metalloorganic procedures for the preparation of 111-V (A"'BV) and I I-VI (A"BV1) semiconductors.' Such studies are motivated by at least two goals: ( 1 ) to develop alternatives to chemical-vapor deposition with group V hydrides for semiconductor-film production and (2) to provide syntheses of semiconductor clusters having sizes and properties intermediate between those of molecular compounds and nonmolecular solids. We describe a new strategy for the synthesis of phosphide semiconductors that is analogous to the sol-gel synthesis of oxides. The latter, a well-established metalloorganic technique, proceeds by hydrolysis of homoleptic alkoxide precursors and polycondensation of the resulting M-OH intermediates2 Our strategy is based on the alcoholysis of homoleptic silylphosphido precursors, M[P(SiMe3),lx, and polycondensation of the resulting M-PH2 intermediates. We now report the synthesis of the title silylphosphido precursors and the preparation of Cd3P2by alcoholysis and polycondensation. We also describe the synthesis of the ternary compounds ZnGeP, and CdGeP, by a related condensation reaction. The precursors were prepared according to eq 1 and isolated as air-sensitive, sublimable, crystalline solid^.^ The solid-state (1) (a) Steigerwald. M. L.; Sprinkle, C. R. J . Am. Cfiem. Soc. 1987, 109, 7200. (b) Steigerwald, M. L.; Alivisatos, A. P.; Gibson, J. M.; Harris, T. D.; Kortan, R.; Muller, A. J.; Thayer, A. M.; Duncan, T. M.;Douglass, D. C.; Brus, L. E. Ibid. 1988, 110,3046. (c) Byrne, E. K.; Parkanyi, L.; Theopold, K. H. Science 1988, 241, 332. (d) Wells, R. L.;Pitt, C. G.; McPhail, A. T.; Purdy, A. P.; Shafieezad, S.; Hallock, R. B. Cfiem. Muter. 1989, I , 4. (e) Healy, M. D.; Laibinis, P. E.; Stupik, P. D.; Barron, A. R. J . Cfiem. Soc., Cfiem.Commun. 1989, 359. (f) Stuczynski, S. M.; Brennan, J. G.; Steigerwald, M. L. Inorg. Cfiem. 1989, 28, 4431. (2) (a) Hubert-Pfalzgraf, L. G. New. J . Cfiem. 1987, 1 1 , 663. (b) Roy, R. Science 1987,238, 1664. (c) Gesser, H. D.; Goswami, P. C. Cfiem.Rev. 1989, 89, 765. ( 3 ) Satisfactory elemental analyses were obtained (C, H, Cd, Zn). "P NMR (ppm, benzene-d,): 1, -183.0 (br s), -237.3 (br s); 2, -180.1 (v br s), -229.5 (v br s). Sublimation point ["C (yield), IO-' Torr]: 1, 140 (50%); 2, 140 (75%).
0002-7863/90/ 15l2-5636$02.50/0
]I2 (i):
Figure I . An
+ 2HP(SiMe3),
-
y2(M[P(SiMe3)2]212+ 2HN(SiMe3), (1) M = Zn ( l ) ,87% M = Cd (2), 90%
Solutions of 2 and methanol gave a light-yellow slurry (
